Analysis of Heat Transfer Regulation and Modification Employing Intermittently Emplaced Porous Cavities

1994 ◽  
Vol 116 (3) ◽  
pp. 604-613 ◽  
Author(s):  
K. Vafai ◽  
P. C. Huang
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
External Surface ◽  
Composite Layer ◽  
Darcy Number ◽  
Interactive Effects ◽  
Temperature Fields ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Inertia Parameter

The present work forms a fundamental investigation on the effects of using intermittently porous cavities for regulating and modifying the flow and temperature fields and therefore changing the skin friction and heat transfer characteristics of an external surface. A general flow model that accounts for the effects of the impermeable boundary and inertial effects is used to describe the flow inside the porous region. Solutions of the problem have been carried out using a finite-difference method through the use of a stream function-vorticity transformation. Various interesting characteristics of the flow and temperature fields in the composite layer are analyzed and discussed in detail. The effects of various governing dimensionless parameters, such as the Darcy number, Reynolds number, Prandtl number, the inertia parameter as well as the effects of pertinent geometric parameters are thoroughly explored. Furthermore, the interactive effects of the embedded porous substrates on skin friction and heat transfer characteristics of an external surface are analyzed. The configuration analyzed in this work provides an innovative approach in altering the frictional and heat transfer characteristics of an external surface.

Flow and Heat Transfer Over a Stretched Microsurface

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Suhil Kiwan ◽  
M. A. Al-Nimr
Keyword(s):  
Heat Transfer ◽  
Friction Coefficient ◽  
Flat Plate ◽  
Skin Friction ◽  
Convection Heat Transfer ◽  
Skin Friction Coefficient ◽  
Slip Parameter ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The convection heat transfer induced by a stretching flat plate has been studied. Similarity conditions are obtained for the boundary layer equations for a flat plate subjected to a power law temperature and velocity variations. It is found that a similarity solution exists only for a linearly stretching plate and only when the plate is isothermal. The analysis shows that three parameters control the flow and heat transfer characteristics of the problem. These parameters are the velocity slip parameter K1, the temperature slip parameter K2, and the Prandtl number. The effect of these parameters on the flow and heat transfer of the problem has been studied and presented. It is found that the slip velocity parameter affect both the flow and heat transfer characteristics of the problem. It is found that the skin friction coefficient decreases with increasing K1 and most of the changes in the skin friction takes place in the range 0<K1<1. A correlation between the skin friction coefficient and K1 and Rex has been found and presented. It is found that cf=23Rex−0.5(K1+0.64)−0.884 for 0<K1<10 with an error of ±0.8%. Other correlations between Nu and K1 and K2 has been found and presented in Eq. 28.

Numerical Research in Effects of Baffles on Heat Transfer Characteristics of a Tunnel Kiln’s Flue Gas Heat Exchanger

2014 ◽  
Vol 953-954 ◽  
pp. 911-914
Author(s):  
Jie Li
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flue Gas ◽  
Temperature Fields ◽  
Heat Transfer Characteristics ◽  
Average Temperature ◽  
Transfer Characteristics ◽  
Air Inlet ◽  
Numerical Research ◽  
High Influence

In order to investigate effects of baffles on heat transfer characteristics of a tunnel kiln’s flue gas heat exchanger, the flow fields and temperature fields in two exchangers, one with baffles and the other without, under operative conditions, are separately simulated by using FLUENT code. According to simulation results, average temperature at the air outlet and average pressure at the air inlet of the exchanger with baffles are separately 67.2°C and 265 Pa, and those in the case of the exchanger without baffles are respectively 60.4°C and 240 Pa. Reasons why the baffles exert high influence on heat transfer characteristics of the exchanger are analyzed. On basis of the data and analysis, two conclusions are drawn: (1) Installation of baffles exerts high influence on heat transfer characteristics of the heat exchanger studied. (2) The reason why the baffles could exert such influence is that the baffles prevent much air from flowing into external zones of the baffles, so in per unit time more air exchanges heat energy with hot walls of heat exchange tubes, which are in internal zones of the baffles.

scholarly journals Turbulent flow and heat transfer characteristics in U-tubes: A numerical study

2009 ◽  
Vol 13 (4) ◽  
pp. 175-181 ◽  
Author(s):  
Khalid Alammar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Turbulent Flow ◽  
Skin Friction ◽  
Skin Friction Coefficient ◽  
Heat Transfer Characteristics ◽  
Local Skin ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

Using the standard k-e model, 3-dimensional turbulent flow and heat transfer characteristics in U-tubes are investigated. Uncertainty is approximated using experimental correlations and grid independence study. Increasing the Dean number is shown to intensify a secondary flow within the curved section. The overall Nusselt number for the tube is found to decrease substantially relative to straight tubes, while the overall skin friction coefficient remains practically unaffected. Local skin friction coefficient, Nusselt number, and wall temperature along the tube wall are presented.

Numerical Investigation of Laminar Flow and Heat Transfer in Micro-Cylinder-Groups

2010 ◽  
Author(s):  
Ning Guan ◽  
Zhigang Liu ◽  
Masahiro Takei ◽  
Chengwu Zhang
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Numerical Study ◽  
Differential Pressure ◽  
Temperature Fields ◽  
Geometrical Parameters ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Pressure Resistance

A numerical study on flow and heat transfer of de-ionized water over in-line and staggered micro-cylinder-groups had been performed with Reynolds number varying in the range from 0 to 150. A 3-D incompressible numerical model was employed to investigate the vortex distributions and the influences of the vortexes on the flow and heat transfer characteristics at low Re numbers in micro-cylinder-groups with different geometrical parameters, including micro-cylinder diameters (100μm, 250μm and 500μm), ratios of pitch to micro-cylinder diameter (1.5 2 and 2.5) and ratios of micro-cylinder height to diameter (0.5, 1, 1.5 and 2), etc. The vortex distributions, the flow and temperature fields, and the relationships among them were investigated by solving the numerical model with the finite volume method. It was found that the vortex number became larger with the increase of pitch ratio, and the change of flow rate distribution affected the heat transfer characteristics apparently. The appearance of vortexes in micro-cylinder-group increased the differential pressure resistance; as a result the total flow resistance in micro-cylinder-groups correspondingly increased. Meanwhile, the local heat transfer coefficients nearby the locations of vortexes greatly increased due to the boundary layer separation, which further enhanced the heat transfer in micro-cylinder-groups. The new correlations which could predict Nusselt number of de-ionized water over micro-cylinders with Re number varying from 0–150 had been proposed considering the differential pressure resistance and the natural convection based on numerical calculations in this paper.

scholarly journals Flow and heat transfer characteristics downstream of a porous sudden expansion: A numerical study

2011 ◽  
Vol 15 (2) ◽  
pp. 389-396 ◽  
Author(s):  
Khalid Alammar
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Darcy Number ◽  
Sudden Expansion ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Maximum Heat Transfer ◽  
Inertia Coefficient

Incompressible, axisymmetric laminar flow downstream of a porous expansion is simulated. Effect of the Darcy number and inertia coefficient on flow and heat transfer characteristics downstream of the expansion is investigated. The simulation revealed circulation downstream of the expansion. Decreasing the Darcy number is shown to decrease the circulation region. The Nusselt number, friction coefficient, and pressure drop are shown to increase, while reattachment and location of maximum heat transfer move upstream with decreasing Darcy number. Similar effects are observed with increasing inertia coefficient.

Analysis of Surface Enhancement by a Porous Substrate

1990 ◽  
Vol 112 (3) ◽  
pp. 700-706 ◽  
Author(s):  
Kambiz Vafai ◽  
Sung-Jin Kim
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Fluid Layer ◽  
Composite Layer ◽  
Darcy Number ◽  
Temperature Fields ◽  
External Boundary ◽  
Porous Substrate ◽  
Frictional Drag ◽  
Practical Applications

Convective flow and heat transfer through a composite porous/fluid system have been studied numerically. The composite medium consists of a fluid layer overlaying a porous substrate, which is attached to the surface of the plate. The numerical simulations focus primarily on flows that have the boundary layer characteristics. However, the boundary layer approximation was not used. A general flow model that accounts for the effects of the impermeable boundary and inertia is used to describe the flow inside the porous region. Several important characteristics of the flow and temperature fields in the composite layer are reported. The dependence of these characteristics on the governing parameters such as the Darcy number, the inertia parameter, the Prandtl number, and the ratio of the conductivity of the porous material to that of the fluid is also documented. The results of this investigation point out a number of interesting practical applications such as in frictional drag reduction, and heat transfer retardation or enhancement of an external boundary.

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